1. Field of the Invention
The invention relates to a medium supplying apparatus.
2. Related Background Art
Conventionally, in an image forming apparatus, for example, a printing apparatus, a copying apparatus or a facsimile apparatus, in order to supply sheets serving as medium, a medium supplying apparatus is installed. The medium supplying apparatus comprises a reversing unit to reverse the sheet for recording on both sides of the sheet.
FIG. 2 is a summary drawing showing a conventional printing apparatus.
In FIG. 2, 11 is a printing apparatus, 12 is a sheet cassette; 13 is a sheet supplying roller which is set at the front end (that is, the right end in FIG. 2) for sending out the sheet (not shown) to a conveyance route Ra; 14 is a conveyance roller for conveying the sheet sent out; 15 is a registry roller, 16 is a photoconductor drum; 16a is a transferring roller set such as pressing upon the photoconductor drum 16; and 17 is a fixing device. The fixing device 17 includes a heating roller 52 and a pressure roller 53.
Further, 18 is a separator which is set at a position a or a position b and is used for making alternatively the conveyance route Ra join with a conveyance route Rb or with a conveyance route Rc; and 19 is a reversing unit used for duplex printing.
The reversing unit 19 includes an upper frame 20 and an under frame 21. On the upper frame 20, a plurality of pinch rollers 22 are installed, and on the under frame 21, a plurality of conveyance rollers are mounted. Further, in the reversing unit 19, a reversing roller 54 is set for reversing the sheet conveyed from the conveyance route Rb and for sending the reversed sheet to a conveyance route Rd.
Moreover, the upper frame 20 is installed at a fulcrum 27 such as opening and shutting freely. When the upper frame 20 is set horizontally at a shut position to face the under frame 21, each pinch roller 22 is pressed against corresponding conveyance rollers 23 by springs (not shown).
Next, the operation of the printing apparatus with the above construction is explained.
To perform duplex printing, first the sheet is sent out from the sheet cassette 12 by the sheet supplying roller 13, and is conveyed to the conveyance route Ra by the conveyance roller 14. Then, the sheet is printed on its one side and is conveyed to the separator 18. At this time, the separator 18 is set at the position a, so the sheet is sent toward the reversing unit 19.
Further, after the sheet is reversed and is conveyed to the conveyance route Rd between the upper frame 20 and the under frame 21 by the pinch rollers 22 and the conveyance rollers 23, the sheet is sent out again by the sheet supplying roller 13 and is conveyed again to the conveyance route Ra by the conveyance roller 14. Then, the sheet is printed again on its other side and is conveyed again to the separator 18. At this time, the separator 18 is set at the position b, so the sheet is sent to the conveyance route Rc and is output to the outside of the printing apparatus 11.
The reversing unit 19 and the upper frame 20 can be locked to the under frame 21. Accordingly, on either of the right end and the left end (in FIG. 2, the front end and the back end) of the under frame 21, a lock lever 26 is mounted such that it rotates around a fulcrum 55. On the lock lever 26, a ditch 56 is formed. Further, corresponding to the ditch 56, a coupling bar 28 is mounted on the upper frame 20.
When the lock lever 26 rotates in a counterclockwise direction, the upper frame 20 is locked. On the contrary, when the lock lever 26 rotates in a clockwise direction, the upper frame 20 is unlocked. Moreover, by using a spring 25 in the lock lever 26, the lock lever 26 is accompanied along the clockwise direction. Thus, when the upper frame 20 rotates to the shut position, the upper frame 20 is locked automatically at the under frame 21.
When the reversing unit 19 is clogged with a sheet, there is a need to pull out the reversing unit 19 from the printing apparatus 11 and to make the lock lever 26 rotate to unlock the upper frame 20 with respect to the under frame 21. Thus, by making the upper frame 20 rotate to an inclining position, i.e. an open position with respect to the under frame 21, it is possible to remove the sheet.
However, in the conventional printing apparatus 11, because the lock lever 26 is set at both ends (in FIG. 2, the front end and the back end) of the under frame 21, it is necessary to use both hands to operate the lock lever 26 for locking or unlocking the upper frame 20. Thus the work for opening or shutting the upper frame 20 is troublesome and the work for removing the sheet is also troublesome.
Furthermore, in the case of using the lock lever 26, because it is needed to couple each ditch 56 with the corresponding coupling bar 28, when either of the ditches 56 is not securely coupled with the corresponding coupling bar 28, it is impossible to lock the upper frame 20 with the under frame 21. Thus, there are some possibilities that the sheet will be sent off-line.